Humans and ancient giant marsupials co-existed for at least 15,000 years, according to new findings that re-ignite the debate over how and when Australia's megafauna became extinct.

Archaeologist Dr Judith Field, of the University of Sydney, says the team's findings put to rest one high-profile theory, that humans arrived in Australia and wiped out the megafauna during a relatively brief 1000-year 'blitzkrieg'.

"In some places people may well have had a role but in other places they had no role at all," she says.

Field says the 6000 year overlap tells us people and megafauna co-existed there over an extended period. And given a conservative estimate of human arrival in Australia at 45,000 years ago, this means the two co-existed for at least 15,000 years.

She says this is incompatible with the blitzkrieg model, proposed by well known palaeontologist Dr Tim Flannery, director of the South Australian Museum.

"Having a long overlap of humans and megafauna refutes the blitzkrieg argument of Tim Flannery," she says.

Field says her latest findings also challenge "simplistic" theories that climate change was to blame for the extinction, or that humans slowly killed off the megafauna over 10,000 years by hunting and burning their habitat.

She believes megafauna may have died out at different times across Australia depending on a complex interaction of factors.

A controversial site

Cuddie Springs was excluded by scientists who in 2001 calculated the broadly accepted date of megafaunal extinction Australia-wide as being 46,500 years ago.

Those scientists, including Flannery and dating expert Dr Bert Roberts of the University of Wollongong, argued that sediments at the site had been disturbed, making it difficult to use the dates of surrounding sediments to date the bones.

Field and team say they have now confirmed that the bones were not moved after death by measuring rare earth elements (REE) contained in them.

REEs are not found in bones during life, but are relatively common in soils. After an animal dies, they get taken up into the bone and leave a permanent fingerprint or memory of the original burial location, says Field.

But Roberts remains unconvinced.

He says the REE technique is generally used for much older deposits and may not be reliable for deposits as relatively young as Cuddie Springs.

Roberts also says there are no articulated (connected) bones at the site, suggesting the site is disturbed.

Field argues the bones are disarticulated because people were butchering and eating the animals, but some bones are found within 10 centimetres of each other.

Roberts says the only thing that would convince him is direct dating of the bones although this is complex, costly and time consuming.

While Roberts thinks Flannery's blitzkrieg model is less likely, rather than more likely, he does believe humans played a role.

Flannery himself declined to comment, referring ABC Science Online to discuss the matter with a geochemistry expert.

Was climate change responsible?

More evidence that points away from human intervention in the extinction of the megafauna comes from Queensland University of Technology research published today supporting the idea that climate change was responsible.

Research in the journal Memoirs of the Queensland Museum led by QUT PhD researcher Gilbert Price studied a 10 metre deep section of creek bed in the Darling Downs region in the state's southeast.

The researchers found 44 species ranging from land snails, frogs, lizards and small mammals to giant wombats and kangaroos.

The researchers say this suggests the extinction of Darling Downs megafauna was caused by a massive shift in climate rather than by the arrival of humans who over-hunted animals or destroyed habitats by burning the landscape.